The present invention relates to systems and apparatus for handling stacks of articles and, in particular, to apparatus for unstacking articles from a stack thereof. The invention has particular application to the unstacking of stacks of partially nested articles, including but not limited to, pallets, trays, pans, baskets, or the like.
In the baking industry, products are commonly handled, stored and shipped in carriers or containers, such as pallets, baskets, pans, trays, or the like. Thus, there is a constant need for handling empty carriers. Commonly they are stacked for storage and the stacks are moved to locations where they are needed, at which location they must be unstacked. Automatic equipment for performing such unstacking operations are well known in the art.
One prior form of unstacking device utilizes a hook which reaches in and grabs the top carrier and pulls it from the stack. The carriers are frequently very shallow carriers having perforated or lattice-work bottoms. When used for unstacking such containers, the prior device has the disadvantage of occasionally reaching too far into the stack and pulling more than one container from the stack. Also, the hook mechanism is usually designed to coact with a perforated bottom pattern of a particular type of container and is not readily adaptable for use with containers having different perforation patterns.
One type of unstacking device which avoids this difficulty is disclosed in U.S. Pat. No. 3,521,763, and utilizes rollers or belts which frictionally engage the edge of the top container and peel it off the stack. While this "peel-off" mode of operation is commonly used in unstacking devices, when it is used with items of substantial mass (as opposed, for example, to sheets of material, such as paper) it is necessary to utilize auxiliary gripping means, such as another belt, roller or the like for gripping the opposite edge of the top item so as to ensure its separation and removal from the stack. This is particularly true in the case of partially nested containers.